Abstract
Introduction
Recently, there are increasing literatures of the in vivo kinematics of total knee arthroplasty (TKA). Those previous studies have been reported in regard of either intra-operative kinematics or post-operative kinematics. However, the direct correlation between intra- and post-operative kinematics of TKA has not been revealed. There are no evidences that intra-operative kinematics can lead to post-operative kinematics.
Purpose
The purpose of this study is to verify the direct correlation between intra- and post-operative kinematics of TKA.
Materials and Methods
We investigated 6 knees (1 male and 4 females; mean age, 74.5 years [range, 69 to 85 years]) implanted with cruciate-retaining TKA caused by osteoarthritis. The one operator evaluated intra-operative passive un-loading kinematics after implanting all components using navigation system by hand throughout knee flexion. The postoperative active loading kinematics was obtained by fluoroscopic images and was analyzed by the 2D/3D registration technique. Both kinematics showed axial rotation angles at 10°intervals of knee flexion. Though flexion angle using navigation system was decided on mechanical axes of femur and tibia, flexion angle using 2D/3D matching method was based on the position of femoral and tibial components. Because the gap of knee flexion angle between both kinematics was approximately 7.3°from postoperative radiographs, we corrected 10°addition to each flexion angle in postoperative kinematics. Moreover, after axial rotational position was changed to axial rotational variation within each interval, we investigated the correlation directly. We noticed also that while the intra-operative kinematics showed axial rotation of tibia against femur showed, the post-operative kinematics showed that of femur against tibia. So, post-operative axial rotations were reversed.
Results
Axial rotational patterns between intra- and post-operative kinematics, which tibial component against femoral component rotated externally in the initial flexion and switched internally from the mid-flexion to the terminal flexion, demonstrated high correlation with 0.786 of Pearson correlation coefficient (p<0.05).
Discussion
To the best of our knowledge, there is no past report of the direct comparison between the in vivo kinematics of TKA intra-operatively and postoperatively. This is a first study to verify the direct correlation between them. In this study, they depended on different indicator, therefore the comparison of the volumes of rotational angles was not beneficial. We investigated the transition patterns of rotational angle variations at every 10°of knee flexion and the correlation between the intra- and post-operative kinematics was excellent in TKA in despite of un-loading and loading. Though this result doesn't always demonstrated high correlation for all cases, it was noted that intra-operative kinematic evaluation using navigation system is useful information to be referred.
Conclusion
We believe that the analysis of intra-operative kinematics using knee navigation system in TKAs will enable to bring us the useful information to predict the postoperative kinematics.
